In previously co-pending application Ser. No. 494,006, now issued as U.S. Pat. No. 3,946,731, titled "APPARATUS FOR EXTRACORPOREAL TREATMENT OF BLOOD", (said patent being incorporated herein by reference as if fully presented as are also my U.S. Pat. Nos. 3,912,455 and 3,774,762) the apparatus disclosed was directed to withdrawal of blood from a patient, extracorporeal treatment of blood for the purpose of altering its physiologic characteristics and reinfusion of the treated blood to provide a patient with substitute or improved bodily functions. As described in patent '731, such extracorporeal circulation requires control of a substantial number of variables, some of the variables being so critical that failure to control them appropriately can result in death of the patient. Also, the number of variables which must be controlled can be sufficiently large so that it can be almost impossible for an attendant to monitor the variables, make decisions as to what adjustments are necessary and then to carry them out, this difficulty rendering it desirable that monitoring and a major portion of the decision-making, at least, be carried out automatically.
It is now seen that apparatus such as described in '731 can be used for a variety of purposes some of which require only portions of said apparatus rather than the entire apparatus with substantial benefit to the patient through improved monitoring and control of the processes carried out by said portions of the apparatus, thereby increasing the reliability of the procedure and reducing the cost of same.
The variables which must be monitored fall into a hierarchy of importance which requires that the most crucially-important variables associated with the safety of the patient can override those of lesser importance. Accordingly, automatic compensation for variation in those parameters of lesser importance can be gauged by response to those parameters designated to be of greater significance to either the patient's safety, primarily, or, secondarily to continuation of the treatment procedure.
While automatic control of procedures has been available for many years, the instrumentation used has been based on analogue techniques. Thus, in proportional control, a controller would be used for adjusting a valve so that the flow through the valve would be proportional to the difference between a measured flow rate and a flow-rate corresponding to a set-point. Initially, the relationship between the valve opening and the deviation from the set-point was based on a mechanical device or an electromechanical device. In a later stage of development, the control method was electronically operated, but was still based on analogue signals throughout. Recently, however, computers have been developed which, in cooperation with sensors providing analogue outputs and ancillary analogue-to-digital and digital-to analogue converters operate completely in a digital mode. Such computers can be programmed for providing control which is far more accurate and reliable than has previously been possible. Moreover, these digital computers have been progressively miniaturized and the cost thereof has been decreased to such an extent that microcomputers dedicated to a specific purpose have become feasible both from the standpoint of carrying out the dedicated task and from the standpoint of cost. Moreover, such microcomputers can be programmed for carrying out a wide variety of procedures and even for modifying the procedures to take account for the needs of specific patients.
As is evident, such computers can readily be designed for receiving signals from and for participating in the control of a patient-care system where the range of procedures to be carried out by the system is limited to a single group or extends over a wide range encompassing those groups under the term "intensive care". Since the computers can be adapted to cooperate with the hardware of the system either for carrying out control operations automatically or for indicating control steps to be taken by an attendant, systems can be readily designed with respect to the specific needs of an institution or of an individual. It can thus be seen that with the advent of the minicomputer, it becomes possible to effect a substantial reduction in the cost of caring for patients and to increase the reliability of the care extended to patients but a design is needed which can readily be matched to a wide variety of needs.